iOS修改截取图片不规范问题

 +(UIImage *) imageCompressForWidth:(UIImage *)sourceImage targetWidth:(CGFloat)defineWidth{
     UIImage *newImage = nil;
     CGSize imageSize = sourceImage.size;
     CGFloat width = imageSize.width;
     CGFloat height = imageSize.height;
     CGFloat targetWidth = defineWidth;
     CGFloat targetHeight = height / (width / targetWidth);
     CGSize size = CGSizeMake(targetWidth, targetHeight);
     CGFloat scaleFactor = 0.0;
     CGFloat scaledWidth = targetWidth;
     CGFloat scaledHeight = targetHeight;
     CGPoint thumbnailPoint = CGPointMake(0.0, 0.0);
     if(CGSizeEqualToSize(imageSize, size) == NO){
         CGFloat widthFactor = targetWidth / width;
         CGFloat heightFactor = targetHeight / height;
         if(widthFactor > heightFactor){
             scaleFactor = widthFactor;
         }
         else{
             scaleFactor = heightFactor;
         }
         scaledWidth = width * scaleFactor;
         scaledHeight = height * scaleFactor;
         if(widthFactor > heightFactor){
             thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
         }else if(widthFactor < heightFactor){
             thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
         }
     }
     UIGraphicsBeginImageContext(size);
     CGRect thumbnailRect = CGRectZero;
     thumbnailRect.origin = thumbnailPoint;
     thumbnailRect.size.width = scaledWidth;
     thumbnailRect.size.height = scaledHeight;

     [sourceImage drawInRect:thumbnailRect];

     newImage = UIGraphicsGetImageFromCurrentImageContext();
     if(newImage == nil){
         NSLog(@"scale image fail");
     }

     UIGraphicsEndImageContext();
     return newImage;
 }